Use .iterator() to save RAM during export

Author: misli

multigtfs/models/base.py

@@ -30,7 +30,6 @@
 logger = getLogger(__name__)
 re_point = re.compile(r'(?P<name>point)\[(?P<index>\d)\]')
 batch_size = 1000
-large_queryset_size = 100000
 CSV_BOM = BOM_UTF8.decode('utf-8') if PY3 else BOM_UTF8
 
 
@@ -365,70 +364,46 @@ def export_txt(cls, feed):
                     cache[field_name][None] = u''
                     model_to_field_name[model_name] = field_name
 
-        # For large querysets, break up by the first field
-        if total < large_queryset_size:
-            querysets = [objects.order_by(*sort_fields)]
-        else:  # pragma: no cover
-            field1_raw = sort_fields[0]
-            assert '__' in field1_raw
-            assert field1_raw in cache
-            field1 = field1_raw.split('__', 1)[0]
-            field1_id = field1 + '_id'
-
-            # Sort field1 ids by field1 values
-            val_to_id = dict((v, k) for k, v in cache[field1_raw].items())
-            assert len(val_to_id) == len(cache[field1_raw])
-            sorted_vals = sorted(val_to_id.keys())
-
-            querysets = []
-            for val in sorted_vals:
-                fid = val_to_id[val]
-                if fid:
-                    qs = objects.filter(
-                        **{field1_id: fid}).order_by(*sort_fields[1:])
-                    querysets.append(qs)
-
         # Assemble the rows, writing when we hit batch size
         count = 0
         rows = []
-        for queryset in querysets:
-            for item in queryset.order_by(*sort_fields):
-                row = []
-                for csv_name, field_name in column_map:
-                    obj = item
-                    point_match = re_point.match(field_name)
-                    if '__' in field_name:
-                        # Return relations from cache
-                        local_field_name = field_name.split('__', 1)[0]
-                        field_id = getattr(obj, local_field_name + '_id')
-                        row.append(cache[field_name][field_id])
-                    elif point_match:
-                        # Get the lat or long from the point
-                        name, index = point_match.groups()
-                        field = getattr(obj, name)
-                        row.append(field.coords[int(index)])
+        for item in objects.order_by(*sort_fields).iterator():
+            row = []
+            for csv_name, field_name in column_map:
+                obj = item
+                point_match = re_point.match(field_name)
+                if '__' in field_name:
+                    # Return relations from cache
+                    local_field_name = field_name.split('__', 1)[0]
+                    field_id = getattr(obj, local_field_name + '_id')
+                    row.append(cache[field_name][field_id])
+                elif point_match:
+                    # Get the lat or long from the point
+                    name, index = point_match.groups()
+                    field = getattr(obj, name)
+                    row.append(field.coords[int(index)])
+                else:
+                    # Handle other field types
+                    field = getattr(obj, field_name) if obj else ''
+                    if isinstance(field, date):
+                        formatted = field.strftime(u'%Y%m%d')
+                        row.append(text_type(formatted))
+                    elif isinstance(field, bool):
+                        row.append(1 if field else 0)
+                    elif field is None:
+                        row.append(u'')
                     else:
-                        # Handle other field types
-                        field = getattr(obj, field_name) if obj else ''
-                        if isinstance(field, date):
-                            formatted = field.strftime(u'%Y%m%d')
-                            row.append(text_type(formatted))
-                        elif isinstance(field, bool):
-                            row.append(1 if field else 0)
-                        elif field is None:
-                            row.append(u'')
-                        else:
-                            row.append(text_type(field))
-                for col in extra_columns:
-                    row.append(obj.extra_data.get(col, u''))
-                rows.append(row)
-                if len(rows) % batch_size == 0:  # pragma: no cover
-                    write_text_rows(csv_writer, rows)
-                    count += len(rows)
-                    logger.info(
-                        "Exported %d %s",
-                        count, cls._meta.verbose_name_plural)
-                    rows = []
+                        row.append(text_type(field))
+            for col in extra_columns:
+                row.append(obj.extra_data.get(col, u''))
+            rows.append(row)
+            if len(rows) % batch_size == 0:  # pragma: no cover
+                write_text_rows(csv_writer, rows)
+                count += len(rows)
+                logger.info(
+                    "Exported %d %s",
+                    count, cls._meta.verbose_name_plural)
+                rows = []
 
         # Write rows smaller than batch size
         write_text_rows(csv_writer, rows)